It is usually thought by emergency physicians that the diagnosis of a pneumothorax is straightforward and easy to make and to treat, but the diagnosis may sometimes pose a challenge. The present report describes a case of a giant pulmonary bulla in a 40-year-old man that progressed to occupy almost the entire left hemithorax and also subsequently ruptured to produce a large left pneumothorax. The giant bulla was diagnosed only as a pneumothorax, and initially managed with a chest tube only. The differentiation between pneumothorax and a giant bulla can be very difficult, and often leads to inaccurate diagnosis and management. This case report demonstrates the clinical presentation of giant bulla and its complications such as pneumothorax and also highlights the difficulty in making this diagnosis and appropriately treating it. In this article, we emphasized how to differentiate between giant bulla and pneumothorax utilizing history, physical examination, and radiological studies including computed tomography (CT) scan.